1. Field of the Invention
The present invention relates generally to pressure gradient pickups or gradient microphones. The invention relates particularly to a capacitor microphone or a dynamic microphone having a diaphragm mounted within a housing and at least one sound entry opening provided in the housing for conducting the sound to the rear side of the diaphragm. Accoustically acting, phase-shifting sections are connected to the sound entry opening in the interior of the housing.
2. Description of the Prior Art
Many types of pressure gradient pickups are known, primarily those having eight-shaped, cardioid, hypercardioid or supercardioid pickup patterns. The mode of operation of such sound pickups and possible embodiments thereof are known in principle from Austrian Pat. No. 248,513 which describes a moving coil microphone having a unilateral pickup effect, and from the two publications by Herbert Grosskopf entitled "Gerichtete Mikrophone mit phasendrehenden Gliedern" (Directional Microphone Having Phase-shifting Sections), FTZ, year 150, Volume 7, 1950, pages 248 to 253, and "Uber Methoden zur Erzielung eines gerichteten Schallempfangs" (Concerning Methods for Obtaining a Directed Sound Reception), Technishe Hausmitteilungen des Nordwesdeutschen Rundfunks (Technical In-house Information of the North-West German Radio), year 4, No. 11/12, 1952, pages 209 to 218.
All the pressure gradient pickups described in the above-mentioned prior art documents and in later documents have at least one sound entry provided in the transducer housing in the form of one or more openings, so that the sound can be conducted to the rear side of the diaphragm, wherein the sound entry is located in a plane which extends parallel to the plane of the diaphragm and is offset toward the transducer end.
The known pressure gradient pickups cannot be mounted in closed housings because such housings would render the one or more sound entry openings ineffective.
It is, therefore, the primary object of the present invention to generate the sound pressure difference formed by the differences in propagation time in front of and behind the diaphragm of the present gradient pickup in such a way that it is possible to mount the pickup in a closed housing and the excellent directional effect of the sound pickup is preserved.